Continuing studies by this laboratory and by others have supported longstanding theories that information processing (or "use") in the developing nervous system may alter synaptic and dendritic parameters. For example, rats reared from weaning in complex environments have more higher order dendrites on neurons from some cortical regions than do rats from social or isolated rearing. Recent studies have suggested that the formation of dendritic branches in adult rats may be affected by maze and discrimination training. A series of studies is in progress to further explore (a) the types and extent of alteration in the rodent nervous system following a broad range of experiences in development and adulthood, (b) the persistence of these alterations, and (c) their correlation with behavioral measures. These brain changes may represent a correlate of information storage in the developing and adult nervous system. Such a finding would have broad implications in both clinical and theoretical areas.